Row names & column names in R

Question

Do the following function pairs generate exactly the same results?

Pair 1) names() & colnames()

Pair 2) rownames()

Answer 1

And another expansion:

# create dummy matrix
set.seed(10)
m <- matrix(round(runif(25, 1, 5)), 5)
d <- as.data.frame(m)

If you want to assign new column names you can do following on data.frame:

# an identical effect can be achieved with colnames()   
names(d) <- LETTERS[1:5]
> d
  A B C D E
1 3 2 4 3 4
2 2 2 3 1 3
3 3 2 1 2 4
4 4 3 3 3 2
5 1 3 2 4 3

If you, however run previous command on matrix, you'll mess things up:

names(m) <- LETTERS[1:5]
> m
     [,1] [,2] [,3] [,4] [,5]
[1,]    3    2    4    3    4
[2,]    2    2    3    1    3
[3,]    3    2    1    2    4
[4,]    4    3    3    3    2
[5,]    1    3    2    4    3
attr(,"names")
 [1] "A" "B" "C" "D" "E" NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA 
[20] NA  NA  NA  NA  NA  NA 

Since matrix can be regarded as two-dimensional vector, you'll assign names only to first five values (you don't want to do that, do you?). In this case, you should stick with colnames().

So there...